The field of this invention relates to lock mechanism for downhole use, and more specifically, to locks used in wireline applications.
Wireline locks have been in use in the oil field for many years. These generally involve outward displacement of dogs into a receiving groove to hang on to a downhole tool. A typical prior art lock is shown in FIGS. 1 and 2. FIG. 2 is a section view through the dog 10. FIG. 2 illustrates that the fishing neck 12 has a ramp surface 14 which in the view of FIG. 1 cams the dogs 10 outwardly into a mating recess for engagement of the downhole tool (not shown). The position in FIG. 1 is retained by a split ring 16. Arrows 18 in FIG. 2 represent the radial forces brought to bear on fishing neck 12 by the dogs 10. Each of the dogs 10 have circumferential contact along the outer surface 20 of the fishing neck 12 thus making the direction of the force imparted from the dogs 10 to the fishing neck 12 occur principally along the normal axis as revealed by arrows 18. Normally, the collapse load placed on the fishing neck 12 represented by arrows 18 is insufficient to collapse the fishing neck 12. Generally speaking, pressure of axial loads on the wireline lock illustrated in FIGS. 1 and 2 load the locking dogs 10 with the result of such dogs 10 are pushed inward. The collapse or bending load applied to the fishing neck 12 is illustrated by arrows 18.
One problem occurs when locks of the prior art as illustrated in FIGS. 1 and 2 are required to sustain high loads by pressure from slam closures at very high flow rates when the lock is used in conjunction with wireline safety valve. The slam closures result in abrupt pressure build up which heighten the magnitude of the bending and collapse force represented by arrows 18. The slam closure phenomenon when combined with very large bore requirements through the lock which in turn results in a very thin cross section for the fishing neck 12 in the area of the dogs 10 which must resist such collapse force, presents a design challenge addressed by this invention.
U.S. Pat. Nos. 4,711,326; 4,762,177; 4,311,196; and 5,174,397 represent prior art known to the Applicants in the area of guidance systems for slips.
Accordingly, one of the objects of the present invention is to be able to accommodate slam closures and other downhole events which greatly heighten the applied stresses to the lock while at the same time avoiding having to lose bore size in order to provide a sufficiently thick wall to avoid collapse of the fishing neck 12. As a result, modifications have been made to the prior art design shown in FIGS. 1 and 2 which constitutes the present invention. The present invention objectives are to allow high loads to be transmitted from the dogs to the fishing neck in question on large sizes under high load situations without fear of collapse of the fishing neck. Those skilled in the art will appreciate the manner in which the invention solves the problem and its advantages by a review of a description of the preferred embodiment below.
A high load wireline lock features a plurality of dogs supported by a fishing neck. Radial loads, transmitted through the dogs when the lock is engaged, are in turn directed into the fishing neck in the manner so as to distribute the load into the wall of the fishing neck. The contact between the dogs and the fishing neck is along sloping surface which minimize the radial forces against the fishing neck and in turn applies forces in a near tangential direction through the wall of the fishing neck thus greatly increasing the load capacity of the wireline lock.